As known, particularly in the technique of chemical, pharmaceutical and like productions, use is made of large filtration chambers, generally consisting of cylindrical vessels comprising a bottom part, which normally--but not necessarily--consists of a flat base, and a dome-shaped top part, such vessels having diameters which vary between 300 and 5000 mm.
The bottom part of these chambers is particularly important, as the separation of the liquids from the solids takes place therein.
The bottom of these filtration chambers normally consists of:
A very thick metal support plate, meant to stand the working pressure--usually between 0.5 bar and over 10 bar--and to bear the load of the material being filtered; the plate comprises at least one outlet for the filtered liquid. The plate also carries a system to support the filter sheet;
A filter sheet bearing onto the support plate, through the system, and generally consisting of punched plates with constant pitch. The punched are normally connected to the support plate along their entire by screws;
A filter bed, bearing onto the filter sheet and generally consisting of wire or synthetic nets, interwoven in such a way as to ensure the of particles having dimensions below the nominal size of the actual net. Such nets are positioned exactly above the filter bed, and hey are tensioned and connected to the support plate by screws or by into a groove.
To allow opening these vessels, the bottom part is normally made disconnectable from the dome-shaped top part. For this purpose, the cylindrical dome and the filtering bottom are each equipped with an coupling flange, having a plurality of through holes to house lightening bolts.
This arrangement, --which is also very well known in other fields, --has the advantage of allowing a positively reliable fastening between the coupling flanges, such as to provide--thanks to the squeezing of an interposed gasket--a perfect seal both for the liquids and for the gases contained in the chamber.
Another known system for locking together the cylindrical dome and the filtering bottom is a bayonet coupling system. In this case, use is made of a rotating ring, operated by pneumatic or hydraulic cylinders, which cooperates with said two flanges; this rotating ring is in fact provided with an upper flange, which opposes the flange of the cylindrical dome, and with a lower flange comprising teeth with upward wedges, which opposes the flange of the filtering bottom being itself provided with wedge-shaped teeth.
When the ring is rotated under the action of the pneumatic hydraulic cylinders, the wedges of the teeth of its lower flange are driven in contact with those of the filtering bottom flange; they thus cause the squeezing of the gasket interposed between the flanges of the filtering chamber, thereby providing the seal.
The need to carry out periodically the cleaning of the filtering parts makes it indispensable to often disassemble, reassemble and lock again the various parts of the filtering bottom. It can be easily understood how these operations, fop a conventional filtering structure of the aforecited type, require very long times in order to be able to unscrew and screw again a high number of screws and/or bolts: for instance, in the case of a 2000 mm diameter chamber, even 200 bolts may be present, since one bolt or screw is normally needed every 150 mm, both to fix the filter sheet and to fix the filter netting bed.
Furthermore, the presence of bolts determines material stagnation points, which is in contrast with the cleaning requirements of the filtration chamber.